The broad objective of the proposed research is to provide a more detailed understanding of the stimulus-driven processes that contribute to auditory perception. We will use the high temporal resolution of event-related potentials (ERPs) in conjunction with behavioral methods to compare the outcome of stimulus-driven auditory processes with the perception resulting from attentive processing of the same sounds, across various experimental conditions. This will allow us to evaluate the processing stages between sensory input and behavioral response. There are three main aims of the proposal. One is to determine the extent of processing of unattended acoustic information. Four experiments address this aim. One tests the processing capacity for unattended sounds. Another determines whether the process of auditory feature integration requires attention. A third tests the hypothesis that the auditory system organizes information from multiple unattended sources when attention is directed to a single acoustic source. The fourth investigates stimulus context effects on auditory event formation. A second aim is to understand how attention and stimulus-driven processes interact. Two experiments address this aim. One investigates how perception relates to stimulus-driven auditory event formation and another, the role of attention in auditory stream formation. The third aim is to investigate effects of attention on early sensory grouping processes. One experiment will test the hypothesis that top-down processing can modify the stimulus- driven sound organization. Deficits in central auditory processing are thought to play a key role in many cognitive disorders (e.g., autism or dyslexia). Using electrophysiological measures, in conjunction with behavioral methods, to delineate the stimulus-driven processes that contribute to auditory perception can help advance our understanding of impaired processing, which is essential for developing rehabilitative treatments. Furthermore, because subject response is not needed for obtaining the ERP components (such as N1 and MMN), this methodology has the potential to be an important non-invasive tool for diagnosis of central auditory processing deficits that contribute to impaired cognition.